1. Field of the Invention
The present invention relates to a head chip to be mounted on an ink-jet recording apparatus applicable, for example, to a printer, a facsimile apparatus, or an on-demand printer, and to a method of producing the head chip.
2. Description of the Related Art
An ink-jet recording apparatus has been known which records characters and images on a recording medium by using an ink-jet head on which there is mounted a head chip having a plurality of nozzles for ejecting ink.
Examples of the conventional ink-jet recording apparatus include a serial type ink-jet recording apparatus in which the nozzles of the head chip are arranged in the ink-jet head so as to be opposed to the recording medium and in which scanning is effected with the ink-jet head in a direction perpendicular to the transporting direction of the recording medium to thereby perform printing, and a line type ink-jet recording apparatus in which the ink-jet head is stationary, printing being effected by moving the recording medium alone.
Examples of the head chip to be mounted on a conventional ink-jet head are disclosed, for example, in JP2000-512233A and JP2000-296618 A (See Patent Documents 1 and 2).
FIGS. 10A and 10B are sectional views showing the conventional head chip as disclosed in the former document.
As shown in FIG. 10A, a head chip 100 comprises: a substrate 120 composed of a substrate main body 121 formed of an insulating material such as alumina and having in one surface thereof a recess, and piezoelectric ceramic members 122 provided in the recess and having a plurality of grooves 125 extending in a direction perpendicular to the longitudinal direction thereof; and a nozzle plate 140 joined to the substrate 120 so as to cover the open side of the recess and having nozzle openings 141.
Formed in the substrate main body 121 are chambers 130 defined by the piezoelectric ceramic members 122 at either end of the recess in the width direction so as to extend in the longitudinal direction.
Further, electrodes 127 are formed on side walls 126 defining the grooves 125 of the piezoelectric ceramic 122, and each electrode 127 is electrically connected to a lead wiring provided on the recess side surface of the nozzle plate 140.
Further, in the bottom surface of the substrate main body 121, there are provided an ink supply hole 131 and an ink discharge hole 132 for supplying and discharging ink to and from each chamber 130.
In this head chip 100, ink is supplied from one chamber 130, and supplied to the other chamber 130 through the grooves 125 of the piezoelectric ceramic 122, whereby ink is supplied to the interior of the grooves 125.
And, by applying voltage to the electrodes 127 provided on the side walls 126, the side walls 126 undergo shear mode displacement, whereby the ink filling the grooves 125 is ejected through the nozzle openings 141.
To perform high speed printing with this head chip 100 with the number of nozzle openings 141 increased, piezoelectric ceramic members 122 with the plurality of grooves 125 are provided side by side in the recess of the substrate main body 121, and the nozzle openings 141 are provided in the areas opposed to the grooves 125, as shown in FIG. 10B, whereby the number of nozzle openings 141 in the head chip 100 is doubled.
In producing this head chip 100, the recess is formed in the substrate main body 122, and the piezoelectric ceramic members 122 with the plurality of grooves 125 are positioned and secured to predetermined positions on the bottom surface of the recess to form the substrate 120, and then the nozzle plate 140 is joined to the substrate to complete the head chip 100.
FIG. 11 shows a head chip as disclosed in the latter document. FIG. 11 is a cut-away perspective view of a main portion of the conventional head chip.
As shown in the drawing, a head chip 200 includes a substrate 220 consisting of a substrate main body 221 formed of an insulating material such as alumina and equipped with a recess 224 open at one end surface and one surface, and piezoelectric ceramic members 222 embedded in the recess 224, wherein a plurality of grooves 225 are defined by side walls 226 so as to extend over the substrate main body 221 and the piezoelectric ceramic members 222 and in the longitudinal direction of the recess 224.
One end portion of each of the grooves 225 formed in the substrate 220 is open at one end surface of the piezoelectric ceramic members 222, and the other end portions thereof extend up to the substrate main body 221 with their depth gradually decreasing.
Further, electrodes (not shown) are provided on the side walls 226 defining the grooves 225 of the piezoelectric ceramic 222, and the electrodes are electrically connected to lead wiring 227a provided in the region of the substrate main body 221 where no grooves 225 are formed.
Further, a nozzle plate 240 having nozzle openings 241 at regions opposed to the grooves 225 is joined to one end surface of the substrate 220 where the grooves 225 are open, and on one side of the substrate 220 where the grooves 225 are open, there is provided an ink chamber 230 communicating with the grooves 225 and adapted to supply ink to the grooves 225. Further, joined to this side of the substrate is an ink chamber plate 231 for sealing the region of the grooves 225 which does not face the ink chamber 230.
In producing this head chip 200, the recess 224 is formed in the substrate main body 221, and the piezoelectric ceramic 222 is embedded in the recess 224 to thereby form the substrate 220, the grooves 225 being formed by simultaneously grinding the substrate main body 221 and the piezoelectric ceramic 222 with a dicer using a disc-shaped dice cutter. And, the electrodes are formed-on the side walls 226 defining the grooves 225, and the lead wiring 227a is formed in the substrate main body 221, the nozzle plate 240 and the ink chamber plate 231 being joined to the substrate to form the head chip 200.
In this head chip 200, the piezoelectric ceramic 222 is embedded in the substrate main body 221, and then the plurality of grooves 225 are formed, so that it is possible to reduce product defects and to achieve an improvement in yield.
In the former type of head chip, however, it is necessary to perform positioning on the piezoelectric ceramic members when fixing them to predetermined positions on the bottom surface of the recess of the substrate main body, and high precision positioning is rather difficult to perform.
Further, in the former type of head chip, when forming grooves in the piezoelectric ceramic members, the side walls defining the grooves are subject to breakage, resulting in poor yield.
In the former type of head chip, the number of nozzle openings can be doubled by arranging the piezoelectric ceramic members side by side in the recess, so that it allows high speed printing in a serial type ink-jet recording apparatus, in which the ink-jet head with the head chip mounted thereon is moved in a direction perpendicular to the transporting direction of the recording medium, whereas, in a line type ink-jet recording apparatus, in which the recording medium is moved with the ink-jet head being stationary, the nozzle opening positions in the row direction are the same in each row of nozzle openings, so that it is impossible to perform high density printing.
On the other hand, in the latter type of head chip, when the number of nozzle openings are to be increased in order to perform high speed printing or high density printing, the head chips have to be arranged side by side, which leads to an increase in head chip size and an increase in cost.
Further, when a conductive ink such as a water-color ink is used in the head chips of both types, adjacent electrodes provided on side walls defining a groove conduct to eliminate the potential difference, with the result that the side walls do not undergo deformation, making it impossible to eject ink.
In view of this, there have been proposed a method according to which the grooves communicating with the nozzle openings and used for ink ejection are arranged at intervals and used as chambers, with the grooves not used for ink ejection being used as dummy chambers, and a method according to which insulating films covering the electrodes are provided on the surfaces of the electrodes in the grooves.
In the former method, in order that the dummy chambers may be filled with no ink and that only the chambers may be selectively filled with ink, there is provided a partition having openings solely in the regions opposed to the chambers, whereby the electrodes provided on the inner surfaces of the side walls of the chambers are used as common electrodes with the same potential in all the chambers. Further, the electrodes on the outer surfaces of the side walls of the chambers are used as individual electrodes for selectively driving the chambers, whereby an electric field is applied to the side wall on either side of the chamber to thereby eject ink.
However, this requires provision and machining of a partition, resulting in a rather high cost.
In the latter method, when dirt or the like generated during the production process exists under the insulating film, the insulating film will be peeled off during use of the head chip.
The present invention has been made in view of the above problems in the prior art. It is an object of the present invention to provide a head chip and a method of producing the same which help to attain an improvement in yield and a reduction in production cost and which allow high speed printing and high density printing.
According to a first aspect of the present invention for solving the above-mentioned problem, there is provided a head chip in which grooves defined by side walls are provided in one surface of a substrate and in which by applying voltage to electrodes provided on the side walls, ink in the grooves is ejected from nozzle openings of a nozzle plate joined to one surface of the substrate,
characterized in that: a plurality of piezoelectric ceramic members extending in a reference direction are embedded in one surface of an insulating main body of the substrate to form the substrate; the grooves are formed at predetermined intervals so as to extend over the row of piezoelectric ceramic members to thereby provide the side walls; the electrodes are provided in the regions of the side walls where the piezoelectric ceramic members are provided to thereby form drive portions for independent driving; and the nozzle openings are provided at positions corresponding to the drive portions of the grooves to form the plurality of nozzle rows.
According to a second aspect of the present invention, in the first aspect of the invention, the head chip is characterized in that: the grooves are formed in a direction inclined by a predetermined angle from a direction perpendicular to the reference direction over the row of piezoelectric ceramic members; and the positions in the reference direction of all the nozzle openings of the plurality of nozzle rows differ from one another.
According to a third aspect of the present invention, in the first or second aspect of the invention, the head chip is characterized in that in the regions of the other surface of the substrate not opposed to the piezoelectric ceramic members, there are formed an ink supply hole for supplying ink to the grooves and an ink discharge hole for discharging the ink in the grooves.
According to a fourth aspect of the present invention, in the third aspect of the invention, the head chip is characterized in that: in the regions of the other surface of the substrate not opposed to the piezoelectric ceramic members, there are formed the plurality of common grooves extending in the same direction as the reference direction and over the direction in which the grooves are arranged side by side and communicating with bottoms of the grooves; and communication holes through which the common grooves communicate with the grooves constitute the ink supply hole and the ink discharge hole.
According to a fifth aspect of the present invention, in the fourth aspect of the invention, the head chip is characterized in that: the grooves are formed by alternately arranging chambers to be filled with ink and dummy chambers to be filled with no ink; and the dummy chambers are shallower than the chambers, whereby the common grooves communicate exclusively with the bottoms of the chambers.
According to a sixth aspect of the present invention, in the fourth aspect of the invention, the head chip is characterized in that the side walls are missing in the regions in contact with the piezoelectric ceramic members.
According to a seventh aspect of the present invention, in any one of the first to sixth aspects of the invention, the head chip is characterized in that: two of the piezoelectric ceramic members are arranged side by side in the substrate; and the electrodes are provided individually on the side walls so as to extend from the ends of the grooves to regions opposed to the drive portions.
According to an eighth aspect of the present invention, in any one of the first to seventh aspects of the invention, the head chip is characterized in that the piezoelectric ceramic members are embedded in the substrate so as to reach the bottoms of the grooves.
According to a ninth aspect of the present invention, in the eighth aspect of the invention, the head chip is characterized in that: the piezoelectric ceramic members exhibit different polarizing directions substantially at the center with respect to the depth direction of the grooves; and the electrodes are provided on the entire surfaces of the side walls where the piezoelectric ceramic members are exposed.
According to a tenth aspect of the present invention, in any one of the first to ninth aspects of the invention, the head chip is characterized in that the end portions of the grooves are formed so as to be gradually reduced in depth.
According to an eleventh aspect of the present invention, in any one of the first to tenth aspects of the invention, the head chip is characterized in that the substrate is formed of a material whose coefficient of linear expansion is substantially the same as that of the piezoelectric ceramic members.
According to a twelfth aspect of the present invention, in any one of the first to eleventh aspects of the invention, the head chip is characterized in that the substrate is formed of a ceramic material such as alumina.
According to a thirteenth aspect of the present invention, there is provided a head chip producing method characterized by including: forming a substrate by embedding the plurality of piezoelectric ceramic members extending in a reference direction in one surface of an insulating substrate main body; forming grooves at predetermined intervals so as to extend over the row of piezoelectric members to thereby form side walls defining the grooves; forming electrodes in the regions of the side walls where the piezoelectric ceramic members are provided to thereby form drive portions for independent driving; and joining a nozzle plate in which nozzle openings are provided at equal intervals and in a plurality of rows at positions corresponding to the drive portions of the grooves to one surface of the substrate.
According to a fourteenth aspect of the present invention, in the thirteenth aspect of the invention, the head chip producing method is characterized in that: in forming the grooves, the grooves are formed in a direction inclined by a predetermined angle from a direction perpendicular to the reference direction; and the positions in the reference direction of all the nozzle openings of the plurality of rows differ from each other.
According to a fifteenth aspect of the present invention, in the thirteenth or fourteenth aspect of the invention, the head chip producing method is characterized in that in embedding the piezoelectric ceramic members in the substrate, recesses of the same size as the piezoelectric ceramic members are formed in the substrate, and then the piezoelectric ceramic members are joined into the recesses.
According to a sixteenth aspect of the present invention, in the thirteenth or fourteenth aspect of the invention, the head chip producing method is characterized in that: in embedding the piezoelectric ceramic members in the substrate, a step-like recess having an upper recess and a lower recess having a step portion larger than the piezoelectric ceramic members is formed in the substrate; and the piezoelectric ceramic members are joined to a bottom surface portion of the lower recess and side surface portions of the lower recess.
According to a seventeenth aspect of the present invention, in any one of the thirteenth to sixteenth aspects of the invention, the head chip producing method is characterized by further including forming, in regions of the other surface of the substrate not opposed to the piezoelectric ceramic members, a plurality of common grooves extending in the same direction as the piezoelectric ceramic members and over the direction in which the grooves are arranged side by side and communicating with the bottom portions of the grooves.
According to an eighteenth aspect of the present invention, in the seventeenth aspect of the invention, the head chip producing method is characterized in that: in forming the grooves, grooves having different depths are alternately formed; and the common grooves are formed so as not to communicate with bottom portions of shallower grooves.
According to a nineteenth aspect of the present invention, in any one of the thirteenth to eighteenth aspects of the invention, the head chip, producing method is characterized in that in embedding the piezoelectric ceramic members in the substrate, the piezoelectric ceramic members are embedded in the substrate so as to reach the bottom surfaces of the grooves.
According to a twentieth aspect of the present invention, in the nineteenth aspect of the invention, the head chip producing method is characterized in that: the piezoelectric ceramic members exhibit different polarizing directions substantially at the center with respect to the depth direction of the grooves; and in forming the drive portions, the electrodes are provided on the entire surfaces of the sidewalls where the piezoelectric ceramic members are exposed.
In the present invention, the plurality of piezoelectric ceramic members are embedded in the substrate main body, and grooves are provided so as to extend over the row of piezoelectric ceramic members, so that the side walls defining the grooves are reliably prevented from being broken during formation of the grooves, thereby making it possible to achieve an improvement in production yield. Further, since the piezoelectric ceramic members are embedded in the substrate main body, there is no need to perform positioning on the piezoelectric ceramic members with respect to the predetermined positions, making it possible to form a high precision head chip with ease.
Further, by providing the plurality of nozzle rows in each of which nozzle openings are arranged side by side, it is possible to realize high speed printing, and, by deviating the position of each nozzle row in the row direction, it is possible to realize high density printing.
Further, by providing ink supply holes for supplying ink to the bottom surfaces of the grooves and alternately arranging grooves with different depths, it is possible to selectively supply ink to the grooves and to use a conductive ink such as a water-color ink.